(1) Field of the Invention
The present invention refers to a copying apparatus and method which is effective when employed in image forming apparatus utilizing the xerographic process.
(2) Description of the Related Art
A conventional xerographic image forming apparatus functions as follows. Charged powdered toner is adhered on a photoconductive layer on the surface of an image carrier which runs endlessly, whereby a transferable toner image is formed on the image carrier. A recording medium, mainly paper, is contacted on the toner image and is given the opposite charge from that of the toner. In this way, the toner image is transferred on the recording medium. The recording medium is separated from the image carrier, and then the toner is fixed on the recording medium. The residual toner and the residual charge on the image carrier are removed. The above process is repeated.
In such a xerographic image forming apparatus, the recording medium remains on the image carrier by static electricity even after image transference. In order to easily separate the recording medium from the image carrier, an AC corona is applied on the recording medium after transference. In this way, the recording medium is given the opposite charge from what was given before transference, and as a result is neutralized. This neutralization promotes good separation of the recording medium from the image carrier. The firmness and elasticity of the recording medium itself also promote good separation. A copying apparatus having the above construction is widely used.
However, paper, which is most widely used as the recording medium, greatly varies in its elasticity and firmness depending on the kind, usage environment, and especially humidity. Therefore, the above separation method cannot necessarily provide constant level of separation.
Further, the above separation method has the following problem. As the total number of copies is increased, toner splashing, paper powder generated by the recording medium, and other foreign substances are adhered on the charging wire of the charger, resulting in decrease or unstableness of discharged current. This means the separation condition deteriorates.